SI-5788 Tailcalls LabelDefs correctly duplicated

... in specialization.

This is a quick hack to get SI-5788 fixed in 2.10.x. The full patch,
which fixes the tailcalls LabelDefs will be merged into trunk, as it's
too late for big changes.

For reference, the complete fix is: e86afe6

Author: VladUreche

src/compiler/scala/tools/nsc/typechecker/Duplicators.scala

@@ -41,7 +41,7 @@ abstract class Duplicators extends Analyzer {
   }
 
   protected def newBodyDuplicator(context: Context) = new BodyDuplicator(context)
-  
+
   def retypedMethod(context: Context, tree: Tree, oldThis: Symbol, newThis: Symbol): Tree =
     (newBodyDuplicator(context)).retypedMethod(tree.asInstanceOf[DefDef], oldThis, newThis)
 
@@ -160,7 +160,7 @@ abstract class Duplicators extends Analyzer {
             newsym.setInfo(fixType(ldef.symbol.info))
             ldef.symbol = newsym
             debuglog("newsym: " + newsym + " info: " + newsym.info)
-          
+
           case vdef @ ValDef(mods, name, _, rhs) if mods.hasFlag(Flags.LAZY) =>
             debuglog("ValDef " + name + " sym.info: " + vdef.symbol.info)
             invalidSyms(vdef.symbol) = vdef
@@ -170,7 +170,7 @@ abstract class Duplicators extends Analyzer {
             vdef.symbol = newsym
             debuglog("newsym: " + newsym + " info: " + newsym.info + ", owner: " + newsym.owner + ", " + newsym.owner.isClass)
             if (newsym.owner.isClass) newsym.owner.info.decls enter newsym
-          
+
           case DefDef(_, name, tparams, vparamss, _, rhs) =>
             // invalidate parameters
             invalidateAll(tparams ::: vparamss.flatten)
@@ -215,7 +215,7 @@ abstract class Duplicators extends Analyzer {
      *  Unless overridden, just returns the tree.
      */
     def castType(tree: Tree, pt: Type): Tree = tree
-    
+
     /** Special typer method for re-type checking trees. It expects a typed tree.
      *  Returns a typed tree that has fresh symbols for all definitions in the original tree.
      *
@@ -278,12 +278,19 @@ abstract class Duplicators extends Analyzer {
           invalidate(rhs)
           ldef.tpe = null
 
-          // since typer does not create the symbols for a LabelDef's params,
-          // we do that manually here -- we should really refactor LabelDef to be a subclass of DefDef
-          def newParam(p: Tree): Ident = {
-            val newsym = p.symbol.cloneSymbol //(context.owner) // TODO owner?
-            Ident(newsym.setInfo(fixType(p.symbol.info)))
-          }
+          // is this LabelDef generated by tailcalls?
+          val isTailLabel = (ldef.params.length >= 1) && (ldef.params.head.name == nme.THIS)
+
+          // the typer does not create the symbols for a LabelDef's params, so unless they were created before we need
+          // to do it manually here -- but for the tailcalls-generated labels, ValDefs are created before the LabelDef,
+          // so we just need to plug in the name
+          def newParam(p: Tree): Ident =
+            if (isTailLabel)
+              Ident(p.symbol.name) // let the typer pick up the right symbol
+            else {
+              val newsym = p.symbol.cloneSymbol //(context.owner) // TODO owner?
+              Ident(newsym.setInfo(fixType(p.symbol.info)))
+            }
           val params1 = params map newParam
           val rhs1 = (new TreeSubstituter(params map (_.symbol), params1) transform rhs) // TODO: duplicate?
           rhs1.tpe = null
@@ -365,7 +372,7 @@ abstract class Duplicators extends Analyzer {
         case EmptyTree =>
           // no need to do anything, in particular, don't set the type to null, EmptyTree.tpe_= asserts
           tree
-        
+
         case _ =>
           debuglog("Duplicators default case: " + tree.summaryString)
           debuglog(" ---> " + tree)
@@ -376,7 +383,7 @@ abstract class Duplicators extends Analyzer {
           super.typed(ntree, mode, pt)
       }
     }
-    
+
   }
 }
 

test/files/pos/SI-5788.scala

@@ -0,0 +1,4 @@
+trait Test {
+  trait B[T]
+  private final def grow[T](): B[T] = grow[T]()
+}